A card shark is an expert card player whose skills enable him to take advantage of weaker players. In poker, the players are often informally graded from fish to shark, which is supposed to reflect how good they are when it comes to understanding the inner workings of the game.
This metaphor is based on the fact that the money tends to flow from inexperienced players to the strongest contenders, creating a poker “food chain” of sorts. A shark might also be a rounder – a player who travels, seeking out high-stakes games.
“Phil Ivey is a real poker shark – he is considered to be one of the most skilled players in the world today and he has emerged victorious in countless tournaments and high stakes ring games.”
The term “shark” originally referred to someone who preys upon others, as in “loan shark.” The term derives from German “Schorke” or “Schurke” (rogue, rascal) and used to have extremely negative connotations – back in 17th century calling someone a card shark (or “card sharp”) was the equivalent of accusing him of being a swindler.
The positive connotations of “expert” and “professional player” did arise later on, however they did not manage to completely supplant the negative ones.